Role of additives (XÂ =Â Ti, Zr) in phase formation and thermal stability of Fe-X-N thin films

In this work we studied the role of additive elements (X = Ti, Zr) on the formation of iron nitride (Fe-N) phases. Amongst all elements, Zr and Ti have the highest affinity towards nitrogen. We added 3.5 at.% Zr, 3.3 at.% and 6.4 at.% Ti in Fe, and prepared a series of Fe-X-N thin films using magnetron sputtering by varying the nitrogen partial pressure (RN2) ranging between 0 and 100%, in steps of 10%. Structural and magnetic properties, and thermal stability of the resulting Fe-X-N thin films were studied. It was found that while the addition of 3.3 at.% Ti results in an enhanced nitrogen incorporation in the Fe-N system, the additions of 6.4 at.% Ti or 3.5 at.% Zr actually results in depletion of nitrogen in the Fe-N system. Further, it was observed that the structural and magnetic stability of the thin films improves significantly with Ti (6.4 at.%) or Zr (3.5 at.%) additions as compared to Ti (3.3 at.%) addition. We find when added in sufficient amount, presence of element X in the grain boundary region leads to a good structural and magnetic stability of Fe-X-N thin films. On the basis of the obtained results, the role of X-N affinity, atomic size of element X, and its amount is discussed in phase formation and thermal stability of Fe-X-N thin films.